1. Field of the Invention
This invention relates to a process for preparing diorganohalogenosilanes. The diorganohalogenosilanes are important compounds in the industry of organosilicon compounds for use as starting materials for imparting reactivity to various types of organopolysiloxanes.
2. Description of the Prior Art
Organohalogenosilanes have been heretofore prepared by the following several processes.
(1) Process wherein silicon powder and alkyl halides or aryl halides are reacted in the presence of a copper catalyst by a so-called direct method, thereby obtaining the diorganohalogenosilanes along with diorganodihalogenosilanes.
(2) Process wherein two types of silicon compounds are subjected to redistribution reaction using amines or Lewis acids to collect the resultant diorganohalogenosilane as set forth in Japanese Laid-open Patent Application Nos. 47-13,314, 49-93,324 and 62-81,390.
(3) Process wherein the Si-Cl bond of chlorosilanes is reduced into a .tbd.SiH bond as described in Japanese Laid-open Patent Application Nos. 52-151,130 and 53-95,922.
The process (1) has now been used on an industrial scale in order to mainly produce diorganodihalogenosilanes. However, even when the type of catalyst and reaction conditions are changed, the production rate of diorganohalogenosilanes is extremely low. Thus, this process is not suitable for the production of diorganohalogenosilanes.
The process (2) fundamentally requires high temperature and high pressure conditions. Accordingly, it involves complicated side reactions through exchange reactions of .tbd.Si--CH.sub.3, .tbd.Si--H and .tbd.Si--Cl, so that the production rate of diorganohalogenosilane is low with an attendant disadvantage that isolation of the diorganohalogenosilane is difficult.
The process (3) makes use of reducing agents which are expensive. In addition, during the reduction of diorganodihalogenosilanes, two chlorine atoms are all reduced with the result that the reaction proceeds to an extent of diorganodihydrosilane. It is difficult to selectively stop the reaction at the stage where diorganohalogenosilanes are produced.
To overcome the disadvantages involved in the process (2), there have been proposed improved processes of preparing diorganohalogenosilanes.
In one such improvement, Japanese Patent Publication No. 52-31,854 proposed a process wherein methylhydrogenpolysiloxane and a diorganodichlorosilane are reacted in the presence of a catalyst, thereby causing an exchange reaction with the hydrogen atom bonded to the silicon atom of the methylhydrogenpolysiloxane. However, this improved process is disadvantageous in that the catalyst and starting materials are expensive and that the yield of a dimethylmonochlorosilane product is low.
Japanese Laid-open Patent Application No. 57-176,911 proposes a process wherein dimethylsilane and dimethyldichlorosilane are subjected to disproportionation reaction similarly to the above process. However, the starting dimethylsilane is expensive. Since dimethylsilane has a boiling point of -20.degree. C. and is gaseous at room temperature, so that it is dangerous and handling of this silane is industrially difficult.